This invention relates to a xerogel, a method of making a xerogel, and a method of treating beverages with a xerogel.
The clarity of beer is an important factor influencing consumer acceptance. The presence of haze in beer is usually associated with inferior quality. Haze in beer is, however, a natural phenomenon and proper treatment is required to prevent or delay its formation. Chill-haze is formed by haze sensitive proteins. Materials that remove haze sensitive proteins should be allowed under the German Purity Law, otherwise known as “Reinheitsgebot”. An alternative to the use of chemical additives in alignment with this law is the use of silica gel that results in removal of haze-sensitive proteins. Finally all materials used for removal of haze sensitive proteins must be removed from the beer.
There are a number of silica based beer stabilisation or clarification agents on the market. They can be divided into two groups, hydrogels and xerogels. Both gels are produced using similar processes as described in many publications, such as U.S. Pat. Nos. 4,515,821; 4,636,394; 5,622,743; and 6,565,905, the entire subject matter of which is incorporated herein by reference. The hydrogels typically include 55 to 70% by weight of water and 45 to 30% by weight of silica with a purity of 99.0% (after calcination). Hydrogels are milled to the desired particle size using common milling techniques. For xerogels, water is typically removed prior to milling using common drying processes, with the resulting xerogels possessing less than about 70 to 80% by weight water. Both gels are generally milled in similar fashion. For both gels, the particle size is adjusted to the desired value using available process control parameters during milling. The inner structure of the gels in terms of surface area, pore volume, pore size distribution, etc., are modified utilizing processing conditions during an aging process of the gels, which typically occurs after formation of the particle and are well known in the literature. Pore volume and surface area are measured using the nitrogen adsorption (BET) at low temperature and calculated using the Kelvin equation (e.g., DIN 66131). For the hydrogels, such parameters are typically not measured in this fashion due to the presence of water in the pores. In addition, drying before measurement is not possible because this process changes the structure of the gel.
Xerogels and hydrogels differ significantly in their behavior in terms of efficiency in stabilisation and filterability. While the xerogels offer high performance in the improvement of stability, the hydrogels are significantly better in the filterability at the same solid concentrations in the beer. Accordingly, it is usually necessary to use two to three times the amount of a hydrogel than would be necessary using a xerogel.
Another important property of a beer stabilisation aid gel relates to the particle size and the particle size distribution. The average particle size of such product that are commercially available typically lies between 5 and 40 microns. Particle size of such gels significantly affects efficiency (i.e., removal/adsorption of haze sensitive high molecular weight proteins) and filterability. A fine sized particle generally possesses good performance in improving the stability but requires additional time for filtration. This relationship typically applies equally for xerogels as for hydrogels.
Important also for the efficiency in terms of stability of beer is the size of accessible surface of the silica. Silica gels are amorphous, inert particulates with open pores and large surface areas. Typically, preferred silica gels are those with high surface areas and large pores, which allow the haze forming molecule to be adsorbed on the silica surface.
Accordingly, there is a need in the industry for a beverage-stabilizing agent that possesses acceptable stabilization properties and is also readily filterable.